MNT silence a LGTM alert (scikit-learn#12633)

Author: qinhanmin2014

sklearn/datasets/openml.py

@@ -6,7 +6,6 @@
 from warnings import warn
 from contextlib import closing
 from functools import wraps
-import warnings
 
 try:
  # Python 3+
@@ -53,9 +52,7 @@ def wrapper():
  except HTTPError:
  raise
  except Exception:
- warnings.warn(
- "Invalid cache, redownloading file",
- RuntimeWarning)
+ warn("Invalid cache, redownloading file", RuntimeWarning)
  local_path = _get_local_path(openml_path, data_home)
  if os.path.exists(local_path):
  os.unlink(local_path)